1. Field of the Invention
The present invention relates to a fuel injection control apparatus in which the fuel injection amount of individual cylinder in a multiple cylinder internal combustion engine is controlled in order to further purify its exhaust gas.
2. Related Background Art
Conventionally, in fuel injection control apparatuses for internal combustion engines, there has been known a technique in which, in view of the fact that the degree of purification of exhaust gas is maximized at the theoretical air/fuel ratio, the air/fuel ratio is detected by an air/fuel ratio sensor (oxygen concentration sensor) disposed in the exhaust system and the fuel injection amount is feedback-controlled such that the detected air/fuel ratio becomes the theoretical air/fuel ratio in order to purify the exhaust gas (Japanese Unexamined Patent Publication Sho No. 59-101562).
Also, there has been known a technique in which a single above-mentioned air/fuel ratio sensor is disposed at the collective portion in the exhaust system of the multiple cylinder internal combustion engine, while a theoretical model of this exhaust system is constructed, and the detected value of the single air/fuel ratio sensor is applied to this theoretical model so as to estimate the air/fuel ratio of individual cylinder and, based on thus estimated value, to feedback-control the air/fuel ratio of individual cylinder to attain the theoretical value, thereby purifying the exhaust gas (Japanese Unexamined Patent Publication Hei No. 5-180040).